But Franken said the situation had become too much of a distraction and would prevent him from fully fulfilling his duties as a senator if he stayed in office.

‘‘But this decision is not about me. It’s about the people of Minnesota,’’ he said. ‘‘It’s become clear that I can’t both pursue the Ethics Committee process and at the same time, remain an effective senator for them.’’

He added: ‘‘I may be resigning my seat, but I am not giving up my voice.’’

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The announcement comes amid a reckoning on Capitol Hill over allegations of sexual harassment against powerful lawmakers.

‘‘Enough is enough,’’ Sen. Kirsten Gillibrand, D-N.Y., said at a news conference. ‘‘We need to draw a line in the sand and say none of it is okay, none of it is acceptable. We as elected leaders should absolutely be held to a higher standard, not a lower standard, and we should fundamentally be valuing women. That is where this debate has to go.’’

When he steps down, a replacement will be appointed by Minnesota’s Democratic governor to serve until the 2018 election.

Franken is expected to make his resignation effective at the end of the month, according to a person familiar with his decision, to give time for the governor and his successor to prepare. That time frame would also allow Franken to stick around for potentially consequential votes on the Republican tax bill, funding the government and potentially the fate of ‘‘dreamers,’’ illegal immigrants brought to the country as children.

The drive to purge Franken, coming a day after Rep. John Conyers, D-Mich., resigned under pressure in the House, was a dramatic indication of the political toxicity that has grown around the issue of sexual harassment in recent months.

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It also stood as a stark - and deliberate - contrast with how the Republicans are handling a parallel situation in Alabama, where Roy Moore, their candidate for U.S. Senate in next week’s special election, is accused by women of pursuing them when they were teenagers and he was in his 30s.

Although most of the alleged actions took place before he was a senator, Franken was becoming a growing liability to his party, and Republicans had seized upon the allegations against him.

At Moore’s Tuesday night rally, conservative pundit Gina Loudon declared that Republicans did not need lectures on morality from Democrats who had struggled with their own sex scandals, and cited both Conyers and Franken.

President Trump, himself the target of multiple allegations of sexual assault, has enthusiastically endorsed Moore, and the Republican Party is once again pouring money into the race after initially pulling back. Leading Senate Republicans have also toned down their negative comments about Moore, saying his fate should be up to the voters of Alabama and - if he is elected - the Senate Ethics Committee.

‘‘I'm looking for where are the Republican voices? Where is their outrage?’’ Sen. Mazie Hirono, D-Hawaii, said on CNN.

Franken pointed to Trump and Moore during his remarks Thursday.

‘‘I of all people am aware that there is some irony in the fact that I am leaving while a man who has bragged on tape about his history of sexual assault sits in the Oval Office and a man who has repeatedly preyed on young girls campaigns for the Senate with the full support of his party’’ he said.

The move by Senate Democrats to oust Franken marked a dramatic turnaround in the fortunes of the onetime ‘‘Saturday Night Live’’ star. The senator from Minnesota had emerged as one of the Trump administration’s sharpest foils on Capitol Hill - and as a potential 2020 presidential contender.

Over the past three weeks, more than a half-dozen women have accused Franken of unwanted advances and touching. He apologized, saying in some cases that he had not intended to give offense and in others that he did not recall events as the women did.

The latest allegation against Franken came in a report published Wednesday by Politico. A former congressional aide whose name was withheld by the publication claimed that Franken had tried to forcibly kiss her after a taping of his radio show in 2006, two years before his election to the Senate.

The woman claimed that Franken had told her, ‘‘It’s my right as an entertainer.’’

Franken denied this allegation and said during his floor speech that he while he did not believe other accusations or remember the encounters in the same way, he wanted to sensitive to the growing national discussion over sexual harassment.

Jacquelyn Martin/Associated Press

Senator Al Franken left the Capitol after speaking on the Senate floor on Thursday.

‘‘I was shocked. I was upset,’’ he said of the allegations against him in recent weeks. ‘‘But in responding to their claims, I wanted to be respectful of that broader conversation because all women deserve to be heard and their experience taken seriously.’’

Franken’s alleged offenses were arguably less serious than those attributed to Moore, or to Conyers, the longest-serving member of Congress, who was accused of demanding sexual favors from the women who worked for him. Until late last week, it appeared that Franken’s fellow Democrats would allow his case to work its way through the Senate Ethics Committee, a process that would take months and perhaps years to reach a resolution.

As recently as Nov. 26, Sen. Richard Durbin, D-Ill., the Senate’s second-ranking Democrat, argued on CNN: ‘‘Al Franken has acknowledged what he did was wrong, and it was wrong. He has also submitted his whole case to the Senate Ethics Committee. I think that was the right thing to do. Let’s have a hearing, an investigation. Let’s let this really reach whatever conclusion it is going to reach, but through a due process.’’

But on Wednesday, Durbin expressed no such forbearance. ‘‘Senator Franken’s conduct was wrong. He has admitted to it. And he should resign from the Senate.’’

Even as Senate Democrats expressed support publicly for leaving Franken’s fate in the hands of the Ethics Committee, his female colleagues were increasingly unsettled as new accusers went public.

‘‘People were at the edge of their patience with this. They'd had enough. One more allegation was going to be it,’’ said one senior aide, who spoke on the condition of anonymity to describe private deliberations.

Another said female Democratic senators had been discussing it among themselves ‘‘on the Senate floor, even in the ladies’ room.’’

‘‘Many people have been talking about this for some time,’’ Sen. Patty Murray (D-Wash.) said. ‘‘It wasn’t coordinated. It just happened.’’

Sen. Susan Collins, R-Maine, who has served in the Senate longer than most of her female colleagues, said it was ‘‘significant that the women on his side of the aisle led the way’’ and added that she believed the latest allegation was ‘‘in some ways the final straw for people.’’

Senate Minority Leader Charles Schumer, D-N.Y., who had stood by his friend in the wake of the allegations, called Franken after the Politico story broke early Wednesday and told him directly he had to resign, according to a person familiar with the call, who added that this came before other senators began calling for him to step down.

Schumer also met with Franken and his wife at the leader’s apartment early afternoon to discuss resigning. The session ended without a firm commitment from Franken to do so, said the source, who was granted anonymity to speak frankly about the private exchange.

In recent days - before Wednesday’s report - Sen. Elizabeth Warren, D-Mass., who has known Franken for nearly two decades, had also told Franken he needed to step down, aides familiar with their discussions said. On Wednesday, Warren issued a short public statement, saying, ‘‘I think he should resign.’’

Franken had staved off public calls for his ouster last week, according to a person who has been in touch with the senator and his staff in recent days.

There was a ‘‘mad rush’’ last week to call on Franken to resign when more allegations surfaced, said the person, who was granted anonymity to speak frankly about private discussions. ‘‘I think that people were talked off the ledge at that point and wanted to recollect and figure out if the Senate Ethics investigation should just move forward.’’

But, ‘‘I'm pretty sure that Al should have known that if there was another story that came out that there'd be a mass exodus away from him.’’

Outside the chamber, growing numbers of Democrats had been making the case that it was untenable for Franken to remain in the Senate if their party hoped to maintain the high ground on the issue.

Among those calling for Franken to step down was Doug Jones, Moore’s Democratic opponent in Alabama.

And though she did not mention Franken by name, House Minority Leader Nancy Pelosi, D-Calif., had declared a policy of ‘‘zero tolerance’’ when she called last week for Conyers to leave the House. On Wednesday, Pelosi declared that she was ‘‘very proud of the fact that people are taking this matter head on and are trusting women who come forward, what they have to say.’’